At Visit 1, patients confirmed to be fulfilling all the inclusion criteria and not meeting any of the exclusion criteria will start the 4-week run-in period. During the entire study period, including the run-in period, the only drug allowed to use in addition to the study drug will be oxitropium (short-acting anticholinergic drug) as relief medication. At the end of the run-in period (Visit 2), subjects eligible for randomisation will be evenly randomised to one of the following two treatment groups and start the 12-week treatment period.